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Username Post: Vacuum Advance- how is it supposed to work?
dcairns
Frequent Contributor
Posts 2036
dcairns
04-04-10 06:45 AM - Post#1892591    

Can somebody explain how vacuum advance is supposed to work and the pluses and minuses of ported vacuum vs manifold vacuum, or not running vacuum advance at all?
I think I know how this all works, but want to get rid of the mental cobwebs
- Dave
1964 Impala 4-door sedan

_________
/ --------------- \
_/ /___________\ \_
/_________|_________\
|OOO ___________ OOO|
\______|====|______/
|_|------------------|_|



Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-04-10 09:08 AM - Post#1892650    

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

dcairns
Frequent Contributor
Posts 2036
dcairns
04-04-10 01:20 PM - Post#1892774    

Thank you for taking the time to write all that up. That really gets it clear in my head and gets to the point of a suspicion I have about the idle quality on my 383 in my 64 Impala. I will try out that Echlin vacuum advance can (cheap enough to try and see). My car seems to idle at about 15” and I was noticing the other day, when I put my finger on the bottom of the vacuum advance can to feel the rod, that it was dithering back and forth along with the idle, which has an erratic dive every so often. I am sure there are other issues, but removing this form the soup will help me find the others.
- Dave
1964 Impala 4-door sedan

_________
/ --------------- \
_/ /___________\ \_
/_________|_________\
|OOO ___________ OOO|
\______|====|______/
|_|------------------|_|



IgnitionMan
Valued Contributor
Posts 3197
04-04-10 04:05 PM - Post#1892872    

VC1808, or, CarQuest 57-7535 (same) works as well, just restrict the pin travel to .086 for the 383 on ALL vacuum advances, and, FULL MANIFOLD VACUUM SOURCING, NO PORTED VACUUM.
Robert H
Forum Newbie
Posts 21
04-04-10 06:07 PM - Post#1892944    

Excellent write-up.
Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-05-10 05:41 AM - Post#1893108    

i just keep it saved on my computer, lol.
no problem, hope it helps!
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

sz0k30
"9th Year" Gold Supporting Member
Posts 362
sz0k30
04-05-10 05:53 AM - Post#1893116    

Mr Sinister,

You sound a lot smarter than just 32 years old. And you can spell! Nice write up. Thanks. What do you do?

Roman
61ragtop
Member
Posts 666
04-05-10 10:00 AM - Post#1893256    

Listen to Mr.Sinister and Ignitionman! I made the change and wow way more responsive, better miliage, and just runs all around way better!!

So limit the advance and hook it up too FULL manifold vacuum and enjoy.....
Petroholic
Contributor
Posts 847
Petroholic
04-05-10 01:27 PM - Post#1893351    

So, run the Echlin #VC-1810 advance can and, set limit the mechanical advance to 20 and run full manifold vacuum, is all there is to it?


Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-05-10 01:50 PM - Post#1893368    

thanks, i think.
i'm a purchasing and facilities manager, but i've been a hot rodder pretty much my whole life. just a hobbyist. i can't take credit for it, guys have been doing this for years, i just listen when the old hot rodders talk. with all the new technology and parts out there, this is one of those things that still works. it's stuff like this that gives you an advantage.
ignition and timing are pretty simple once you understand how they work.
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-05-10 02:02 PM - Post#1893374    

petroholic: yep, pretty much it. you only need to back your mechanical advance off enough to prevent pinging, if present, as vacuum advance only applies to part-throttle operation. the old "32-36 degrees at 3000" rule still applies, and the vacuum can won't affect that. all this assumes you're running 93 octane.
you only need the can if you have low idle vacuum, particularly in gear. most stock style hei cans and even the msd cans are designed to work with 15 inches of vacuum at idle, so while running the low vacuum can won't hurt you, you may not need it.
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-05-10 03:25 PM - Post#1893425    

after chatting with grumpyvette, it got my gears turning. so i thought i'd add some more info.

one of the main reasons that you need a little more timing at idle and just off idle is that you are not filling the cylinders. when the engine is at low rpm, the throat of the carb is nearly closed, not letting much air into the cylinders. it's not filling the cylinders with the intake partially or almost fully restricted and thus when it's compressing the mix, there's less to compress, so there are much lower compression pressures. that lightly compressed mixture, inefficient to begin with as far as ideal A/F ratio, will burn more slowly than a highly compressed, mixed, swirled mixture at a more open throttle position. the charge physically can't mix as well as it does at higher rpms, as not only is there less air and fuel to mix, but the velocity of the incoming charge is lower. the lean mixture takes longer to burn, creating more heat in the cylinder, causing pre-ignition or pinging, which is your air/fuel charge being ignited by the hot spot in the cylinder, and not the spark plug, where and when it should be.

for instance, if you light a fire from many places, it will burn faster than if you light it at one. this may help explain why better fuel atomization (and a wider spray pattern in a fuel injected engine, that covers more of the cylinder) will burn faster. there are more air and fuel molecules to mix and ignite, where in lean mixtures, there are less.

check this video out: http://www.youtube.com/watch?v=cy_yaAOKjA8

you will see that the ignition of the charge is focused more on one side, which takes longer to burn the entire mixture because it has to travel to the leaner side of the chamber and ignite the more widely spaced air and fuel particles. had the incoming charge been more uniform and been able to ignite in a wider pattern across the cylinder, it would burn faster. so, less air/fuel mixture to burn, the longer it takes to burn it.

thus, beginning the burn earlier in the process gives the cylinder more time to burn the lean mixture, leading to a more complete burn and better low rpm combustion, which i can personally attest to. to be very unscientific, with less timing at idle, my engine smells very rich, with more timing, the rich smell is gone. it's because the lean charge, which wasn't burning quickly enough at low rpm, is now being combusted more completely. idle mixture has some affect by adding or subtracting fuel to the incoming air, but it's a fine tuning that should be done after your timing is set. this is why everyone will tell you, changing the settings on your carb means nothing if your timing isn't right.
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

NYH1
Contributor
Posts 708
04-05-10 03:52 PM - Post#1893448    

Mr. Sinister, great write up. I'm going to be putting my motor back into my Camaro as soon as I get my transmission rebuilt.

I've honestly never understood vacuum advance. My last Camaro was more of a racecar then a street car. I didn't even use the vacuum advance. This one is going to be driven almost daily and I'm definitely going to use the vacuum advance. I want to be able to tune it the best I can.

The information you posted is going to help a lot!



'78 Camaro, mild Vortec head 385 stroker, 9.1 comp. Lunati Voodoo 262/268 hyd. ft. cam, RPM Intake, 650 AVS carb, TH350 Coan 11" 2600 stall, 8.5" 10 bolt. 3:42 posi, 1 5/8" Full length Headers, 2 1/2" Flowmaster Exhaust System.

Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-05-10 03:55 PM - Post#1893450    

glad it's helping folks and good luck with your camaro!!
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

IgnitionMan
Valued Contributor
Posts 3197
04-05-10 04:24 PM - Post#1893473    

NOPE, one thing not confirmed, LIMIT THE AMOUNT OF PULL PIN TRAVEL ON THE VACUUM ADVANCE, or, there will be way too much vacuum advance timing when it is plugged into full manifold vacuum.

For a 383, 8 crankshaft degrees is all needed to supplement the initial timing, and that is limiting the pull pin to .086 of an inch travel.

If anyone wants pictures of a stop YOU can make at home, and how to measure the stop distance, send me an e/mail. Let me know which type of distributor you have, large cap HEI, or small cap points type, ask for the vacuum advance stop pics, and they will come to you at no charge, no obligation. Use this e/mail address:

info@davessmallbodyheis.com

And, the whole timing and vacuum advance dissertation above, "TIMING AND VACUUM ADVANCE 101", came from a former GM development engineer, another person who also posts here, but did not add to this topic.
Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-05-10 04:37 PM - Post#1893489    

ignitionman: this applies only to the aftermarket can?
i have an msd pro-billet rtr distributor, and as far as i know, msd does not make a can the fully deploys at lower vacuum, so i have to find a can that is compatible. i have been talking with a guy on another board that is playing with using a counter spring to have the same affect as a low vacuum can, so i'm waiting to see where that goes. otherwise, i'll be using an aftermarket can as well.

what changes would need to be made for a smaller engine? say like a 350 or a 327? the problem i've run into with my stock msd can, is not being able to get the idle down in park/neutral (1100-1200 after adjusting the idle screw, idle mixture has NO effect) and not being able to get it up in gear (hovers around 500, BADLY chugging the engine). apart form idle issues, response and low end power are greatly improved, with a noticeable reduction in that "rich" smell out the tailpipes. the only variable left if the low vacuum can, which i have yet to replace.

and yes, that writeup has been around for quite a while, i don't try to take credit for it.
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-05-10 04:57 PM - Post#1893508    

here's the original discussion i read on the subject. http://www.hotrodders.com/forum/vacuum-advance- hoo...
the article has been posted and reposted many, many times on many different forums and has been proven time and time again. i had not read about ignitionman's pointer about limiting pin travel before, so it's probably worth checking into.
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

Trucked_up
Valued Contributor
Posts 4948
04-06-10 02:06 AM - Post#1893671    

  • Quote:
After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark",


Who ever wrote that never worked on older vehicles.many,probably almost all used ported vacuum,cars and trucks.
But the full vacuum does work nice on a hi performance street engine.

Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-06-10 07:17 AM - Post#1893778    

yeah, switching to full manifold vacuum probably doesn't do much for a stock engine, it's definitely more for performance applications.
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-06-10 08:21 AM - Post#1893796    

also, it depends on how old you're talking, my dad's 59 vette is 100% original and has a hollow carb stud that the vacuum line for the advance hooks up to, to draw full manifold vacuum. from my understanding, this was pretty common. in all my reading, ported vacuum became commonplace on emissions era cars.
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

Rick_L
Honored Member
Posts 27220
Rick_L
04-06-10 08:44 AM - Post#1893807    

"yeah, switching to full manifold vacuum probably doesn't do much for a stock engine, it's definitely more for performance applications."

Trust me, they ALL like full manifold vacuum.

The only reason the ported vacuum was used, along with very little initial timing, was smog engines of the 70s and early 80s needed a lot of heat in the exhaust to make the early catalytic converters work. It wasn't for performance, economy, or driveability, because it hurt all three.

Now that cats have advanced a bit, the carmakers run a "normal" amount of vacuum advance, it's just programmed into the engine computer instead of being analog.
steeler_fan
Contributor
Posts 142
steeler_fan
04-06-10 11:13 AM - Post#1893880    


This is article from another board. it explains in detail the operation of Vacuum cans and give information on cans availabe. With this you can find the vacuum that a can will engage and the amount of vacuum timing added.


Distributor Vacuum Advance Control units
Specs and facts for GM Distributors

by Lars Grimsrud
SVE Automotive Restoration
Musclecar, Collector & Exotic Auto Repair & Restoration
Broomfield, CO Rev. B 8-19-02


I’ve been seeing a lot of discussion and questions regarding distributor vacuum advance control units; what do they do, which ones are best, what was used on what, etc., etc. To clarify some of this, I thought I’d summarize a few facts and definitions, and provide a complete part number and specification listing for all vacuum advance control units used by Chevrolet on the points-style distributors. I’m also providing a listing of the specs for all other GM (non-Chevrolet) control units, but without the specific application listed for each (it would take me a bit too much time to research each part number by application across each of the GM Motor Divisions – it took me long enough to compile just the Chevy stuff…!). This latest revision to this paper also includes the HEI listings (the HEI distributors use a longer control unit, so the non-HEI and HEI vacuum advance control units CANNOT be interchanged).

As always, I’m going to include the disclaimer that many of these are my own comments and opinions based on my personal tuning experience. Others may have differing opinions & tuning techniques from those presented here. I have made every attempt to present factual, technically accurate data wherever possible. If you find factual errors in this information, please let me know so I can correct it.

Background
The vacuum advance control unit on the distributor is intended to advance the ignition timing above and beyond the limits of the mechanical advance (mechanical advance consists of the initial timing plus the centrifugal advance that the distributor adds as rpm comes up) under light to medium throttle settings. When the load on the engine is light or moderate, the timing can be advanced to improve fuel economy and throttle response. Once the engine load increases, this “over-advance” condition must be eliminated to produce peak power and to eliminate the possibility of detonation (“engine knock”). A control unit that responds to engine vacuum performs this job remarkably well.

Most GM V8 engines (not including “fast-burn” style heads), and specifically Chevys, will produce peak torque and power at wide open throttle with a total timing advance of 36 degrees (some will take 38). Also, a GM V8 engine, under light load and steady-state cruise, will accept a maximum timing advance of about 52 degrees. Some will take up to 54 degrees advance under these conditions. Once you advance the timing beyond this, the engine/car will start to “chug” or “jerk” at cruise due to the over-advanced timing condition. Anything less than 52 degrees produces less than optimum fuel economy at cruise speed.

The additional timing produced by the vacuum advance control unit must be tailored and matched to the engine and the distributor’s mechanical advance curve. The following considerations must be made when selecting a vacuum advance spec:

How much engine vacuum is produced at cruise? If max vacuum at cruise, on a car with a radical cam, is only 15 inches Hg, a vacuum advance control unit that needs 18 inches to peg out would be a poor selection.

How much centrifugal advance (“total timing”) is in effect at cruise rpm? If the distributor has very stiff centrifugal advance springs in it that allow maximum timing to only come in near red-line rpm, the vacuum advance control unit can be allowed to pull in more advance without the risk of exceeding the 52-degree maximum limit. If the engine has an advance curve that allows a full 36-degree mechanical advance at cruise rpm, the vacuum advance unit can only be allowed to pull in 16 more degrees of advance.

Are you using “ported” or “manifold” vacuum to the distributor? “Ported” vacuum allows little or no vacuum to the distributor at idle. “Manifold” vacuum allows actual manifold vacuum to the distributor at all times.

Does your engine require additional timing advance at idle in order to idle properly? Radical cams will often require over 16 degrees of timing advance at idle in order to produce acceptable idle characteristics. If all of this initial advance is created by advancing the mechanical timing, the total mechanical advance may exceed the 36-degree limit by a significant margin. An appropriately selected vacuum advance unit, plugged into manifold vacuum, can provide the needed extra timing at idle to allow a fair idle, while maintaining maximum mechanical timing at 36. A tuning note on this: If you choose to run straight manifold vacuum to your vacuum advance in order to gain the additional timing advance at idle, you must select a vacuum advance control unit that pulls in all of the advance at a vacuum level 2” below (numerically less than) the manifold vacuum present at idle. If the vacuum advance control unit is not fully pulled in at idle, it will be somewhere in its mid-range, and it will fluctuate and vary the timing while the engine is idling. This will cause erratic timing with associated unstable idle rpm. A second tuning note on this: Advancing the timing at idle can assist in lowering engine temperatures. If you have an overheating problem at idle, and you have verified proper operation of your cooling system components, you can try running manifold vacuum to an appropriately selected vacuum advance unit as noted above. This will lower engine temps, but it will also increase hydrocarbon emissions on emission-controlled vehicles.

Thus, we see that there are many variables in the selection of an appropriate control unit. Yet, we should keep in mind that the control unit is somewhat of a “finesse” or “final tuning” aid to obtain a final, refined state of tune; we use it to just “tweak” the car a little bit to provide that last little bit of optimization for drivability and economy. The vacuum advance unit is not used for primary tuning, nor does it have an effect on power or performance at wide open throttle.

With these general (and a little bit vague, I know…) concepts in mind, let’s review a few concepts and terms. Then it’s on to the master listing of specs and parts…..:

Part Number
There are many different sources for these control units. Borg Warner, Echlin, Wells, and others all sell them in their own boxes and with their own part numbers. Actually, there are very few manufacturers of the actual units: Dana Engine Controls in Connecticut manufactures the units for all three of the brands just mentioned, so it doesn’t make much difference who you buy from: They’re made by the same manufacturer. The part numbers I have listed here are the NAPA/Echlin part numbers, simply because they are available in any part of the country.

ID#
Every vacuum advance control unit built by Dana, and sold under virtually any brand name (including GM), has a stamped ID number right on top of the mounting plate extension. This ID, cross referenced below, will give you all specifications for the unit. So now, when you’re shopping in a junkyard, you’ll be able to quickly identify the “good” vs. the “bad” control units.

Starts @ “Hg
Vacuum is measured in “inches of Mercury.” Mercury has the chemical symbol “Hg.” Thus, manifold vacuum is measured and referred to as “Hg. The “Start” spec for the control unit is a range of the minimum vacuum required to get the control unit to just barely start moving. When selecting this specification, consideration should be made to the amount of vacuum that a given engine produces, and what the load is on the engine at this specification. For example, an engine with a very radical cam may be under very light load at 7 inches Hg, and can tolerate a little vacuum advance at this load level. Your mom’s Caprice, on the other hand, has such a mild cam that you don’t want the vacuum to start coming in until 9 – 10 inches Hg. For most street driven vehicle performance applications, starting the vacuum advance at about 8” Hg produces good results.

Max Advance
Since the vacuum advance control unit is a part of the distributor, the number of degrees of vacuum advance is specified in DISTRIBUTOR degrees – NOT crankshaft degrees. When talking about these control units, it is important that you know whether the person you’re talking to is referring to the distributor degrees, or if he’s talking crankshaft degrees. All of the listings shown in the following chart, and in any shop manual & technical spec sheet, will refer to distributor degrees of vacuum advance. You must DOUBLE this number to obtain crankshaft degrees (which is what you “see” with your timing light). Thus, a vacuum advance control unit with 8 degrees of maximum advance produces 16 degrees of ignition advance in relationship to the crankshaft. When selecting a unit for max advance spec, the total centrifugal timing at cruise must be considered. Thus, a car set up to produce 36 degrees of total mechanical advance at 2500 rpm needs a vacuum advance control unit producing 16 degrees of crankshaft advance. This would be an 8-degree vacuum advance control unit.

Max Advance @ “Hg
This is the range of manifold vacuum at which the maximum vacuum advance is pegged out. In selecting this specification, you must consider the vacuum produced at cruise speed and light throttle application. If your engine never produces 20” Hg, you better not select a control unit requiring 21” Hg to work.

The following listing (Non-HEI) is as follows: The first two part number listings are the two numbers that are most commonly used in a Chevrolet performance application. The “B1” can is the most versatile and user-friendly unit for a good performance street engine. As you can see, it was selected by GM for use in most high performance engines due to its ideal specs. The “B28” can was used on fuel injected engines and a few select engines that produced very poor vacuum at idle. The advance comes in very quick on this unit – too quick for many performance engines. Do not use this very quick unit unless you have a cam/engine combination that really needs an advance like this. It can be used as a tuning aid for problem engines that do not respond well to other timing combinations, and can be successfully used in applications where direct manifold vacuum is applied to the can (see paragraph and discussion on this above)

After this, the listing is by Echlin part number. The Chevrolet applications are listed first by application, followed by a complete listing of all of the units used on any GM product (all GM units are interchangeable, so you can use a Cadillac or GMC Truck unit on your Vette, if that’s what you want to do).

Non-HEI Distributors:

P/N ID# Application Starts @ “Hg Max Adv
(Distr. Degrees @ “Hg.)

VC680 B1 1959 – 63 All Chevrolet 8-11 8 @ 16-18
1964 Corvette exc. FI
1964 Impala, Chevy II
1965 396 High Perf.
1965-67 283, 409
1966-68 327 exc. Powerglide
1967-68 All 396
1969 Corvette 427 High Perf.
1969 396 Exc. High Perf.
1969 Corvette 350 TI
1969-70 302 Camaro
1970 400 4-bbl
1970 396 High Perf.
1970 Corvette 350 High Perf.
1973-74 454 Exc. HEI

VC1810 B28 1965 409 High Perf. 3-5 8 @ 5.75-8
1965 327 High Perf.
1966 327 High Perf.
1964-67 Corvette High Perf. FI

------------------------- ------------------------- ------------------------- ------------------------- ------------------------- ---------------

VC1605 B9 1965 impala 396 Exc. High Perf. 7-9 10.3 @ 16-18
1965 327 All Exc. FI
1969 327 Camaro, Chevelle, Impala
1969-70 Corvette 350 Exc. High Perf.
1969-70 350 4-bbl Premium Fuel
1970 350 Camaro, Chevelle, Impala High Perf.
1971-72 350 2-bbl AT
1971-72 307 All

VC1675 B13 1968 327 Camaro Powerglide 9-11 8 @ 16-18
1968 327 Impala AT
1968 307 AT
1968 302, 307, 327, 350 Camaro, Chevy II
1970 350 Camaro, Chevelle Exc. High Perf.

VC1760 B19 1969 350 Camaro, Chevelle, Impala 4-bbl 5.5-8 12 @ 14-18
1969-70 350 2-bbl

VC1765 B20 1965 396 Impala High Perf 5-7 8 @ 11-13
1966-67 Corvette Exc. High Perf.
1966-67 Impala 427 Exc. High Perf.
1966-68 327 Powerglide Exc. High Perf.
1969 307 All
1969-70 396, 427 Camaro, Chevelle High Perf.
1970 400 2-bbl
1970 307 MT
1973 Camaro 350 High Perf.

VC1801 B21 1971 350 2-bbl 7-9 10 @ 16-18
1971-72 400, 402
1971-72 307 AT

VC1802 B22 1971-72 350 4-bbl 7-9 8 @ 14-16


Other Part Numbers & Specs:

VC700 B3 8-10 11.5 @ 19-21
VC1415 M1 6-8 10 @ 13-15
VC1420 M2 5-7 11 @ 16-17
VC1650 B12 8-10 10 @ 15-17
VC1725 B18 8-10 12 @ 13-16
VC1740 A5 6-8 12 @ 15-17.5
VC1755 A7 8-10 12.5 @ 18-20.5
VC1804 B24 6.5-8.5 10 @ 12-14
VC1805 M13 6-8 12 @ 14.5-15.5
VC1807 B25 5-7 8 @ 13-15
VC1808 B26 5-7 8 @ 11-13
VC1809 B27 5-7 9 @ 10-12
VC1812 B30 5-7 12 @ 11.75-14



The following listing (HEI) is as follows: The first four part number listings are the 4 numbers that are most commonly used in a Chevrolet performance application. The “AR12” can is the most versatile and user-friendly unit for a good performance street engine. The AR 15 and AR23 are almost identical, with only slight variations in their “start-stop” specs. The “AR31” can is the HEI equivalent to the “B28” Hi-Perf can used on the early engines: The advance comes in very quick on this unit – too quick for many performance engines. Do not use this very quick unit unless you have a cam/engine combination that really needs an advance like this. It can be used as a tuning aid for problem engines that do not respond well to other timing combinations, and can be successfully used in applications where direct manifold vacuum is applied to the can (see paragraph and discussion on this above)

After this, the listing is by Echlin part number. All GM HEI vacuum advance units are interchangeable, so you can use a Cadillac or GMC Truck unit on your Vette, if that’s what you want to do.

HEI Distributors:

P/N ID# Application Starts @ “Hg Max Adv
(Distr. Degrees @ “Hg.)

VC1838 AR12 1975 350 Buick 7-9 7 @ 10-12

VC1843 AR15 1977 305 All Exc. Hi Alt, Exc, Calif. 3-5 7.5 @ 9-11
1974 400 All w/2-bbl
1977 305 El Camino
1976 262 Monza Exc. Calif
1976 350 Vette Hi Perf, Incl. Calif
1975 350 Z-28
1977 305 Buick Skylark

VC1853 AR23 1976 350 All Calif. 5-7 7.5 @ 11-12.5
1976 350 Vette Calif., Exc. Hi Perf
1976 400 All, Exc. Calif
1975 350 4-bbl
1974 350 All w/1112528 Distr.
1978 350/400 Heavy Duty Truck, Exc. Calif, Exc. Hi Alt.

VC1862 AR31 2-4 8 @ 6-8

NYH1
Contributor
Posts 708
04-06-10 11:58 AM - Post#1893896    

So would I be better off using an aftermarket adjustable vacuum advance set up like the Crane version or one of the factory cans listed above?

I built a mild 385 stroker motor (4.040" bore x 3.750" stroke). Compression ratio's are SCR 9.1 and DCR 7.93 with the cam I'm using. Which is a Lunatic Voodoo 262/268 Hydraulic Flat Tappet Cam, 219/227 dour. @.050", .468/.489 lift, 112 LSA 1400-5800 RPM range PT# 60102.

I'm using Summit Vortec Heads with a Edelbrock Vortec Performer RPM intake and for now a Holey 80457 600 CFM carb until I get an Edelbrock 650 AVS.

I'm going to use THIS MSD HEI ignition upgrade kit. I want a clean look and don't want to use an "MSD" type external ignition box. My distributor is in pretty good condition. I also have to get a spring kit to set up my machanical advance.

I've read that motors with Vortec heads only like 32° to 34° of total timing. Is that true?

'78 Camaro, mild Vortec head 385 stroker, 9.1 comp. Lunati Voodoo 262/268 hyd. ft. cam, RPM Intake, 650 AVS carb, TH350 Coan 11" 2600 stall, 8.5" 10 bolt. 3:42 posi, 1 5/8" Full length Headers, 2 1/2" Flowmaster Exhaust System.

Huneycutt
Forum Newbie
Posts 21
Huneycutt
04-06-10 02:09 PM - Post#1893952    

I recently did a lot of testing with an HEI ignition on the dyno, including with and without the vacuum advance. Admittedly, the vacuum advance is more for road manners than all out power, but if you are interested, there's a video with all the info here:

http://streetmuscleaction .com/engines/hei/

I think the vacuum advance testing is in the second one.
www.HorsepowerMonster.com

Jim_Elliott
Senior Member
Posts 250
04-06-10 02:58 PM - Post#1893969    

  • Mr. Sinister Said:
yeah, switching to full manifold vacuum probably doesn't do much for a stock engine, it's definitely more for performance applications.



Nope...
On my motor home with a 454 it makes that critter sing right along from the initial startup, Just make sure you have corrected the vacuum advance..
My V.A. is now 11º with a 22º mechanical advance and 11º base timing (8.5 to 9.2 MPG and strong on the hill climba..

Jim

IgnitionMan
Valued Contributor
Posts 3197
04-06-10 06:16 PM - Post#1894089    

Howdy, Jim, glad to see you posting.

NOPE, full manifold vacuum advance, more correctly referred to what it really is, a LOAD COMPENSATION DEVICE, should be on full manifold vacuum, IF THE ENGINE DOES NOT HAVE A FUNCTIONING EGR VALVE. If the engine DOES have a functioning EGR valve, ported vacuum sourcing is just fine, as that emissions laden engine is not set up for any kind of performance, nor good stock operation. It's as simple as that.

And, for ANY and ALL vacuum advances, there should be a positive stop on the pull pin, so the load compensator will NOT over time the engine, NO MATTER HOW THE ENGINE IS SET UP, STOCK TO HOT ROD.
Petroholic
Contributor
Posts 847
Petroholic
04-06-10 06:40 PM - Post#1894113    

Anyone know where I can get one of those Crane cans?


Mr. Sinister
Contributor
Posts 555
Mr. Sinister
04-07-10 03:00 AM - Post#1894227    

summit or jegs sells a few different adjustable cans.
Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

C10 Sleeper
Valued Contributor
Posts 3426
C10 Sleeper
04-07-10 07:58 AM - Post#1894356    

I bought a Crane VA at the local kragen auto parts store.
http://photobucket.com/C10Pictures

NYH1
Contributor
Posts 708
04-07-10 12:21 PM - Post#1894461    

No one answered my question. Would I be better off using one of the V/A cans that steeler_fan posted, or an aftermarket can like the Crane can?

Thanks!

'78 Camaro, mild Vortec head 385 stroker, 9.1 comp. Lunati Voodoo 262/268 hyd. ft. cam, RPM Intake, 650 AVS carb, TH350 Coan 11" 2600 stall, 8.5" 10 bolt. 3:42 posi, 1 5/8" Full length Headers, 2 1/2" Flowmaster Exhaust System.

NYH1
Contributor
Posts 708
04-07-10 01:33 PM - Post#1894487    

IgnitionMan, e-mail sent.
'78 Camaro, mild Vortec head 385 stroker, 9.1 comp. Lunati Voodoo 262/268 hyd. ft. cam, RPM Intake, 650 AVS carb, TH350 Coan 11" 2600 stall, 8.5" 10 bolt. 3:42 posi, 1 5/8" Full length Headers, 2 1/2" Flowmaster Exhaust System.

Jim_Elliott
Senior Member
Posts 250
04-07-10 02:39 PM - Post#1894533    

Thank you Dave, Yes I still read the site and pickup tidbits of information...
I made a test long ago on the EGR valve right before my 87 motor home (454) was sold so here is what was discovered.....
On long pulls my vacuum was 6 inches on the westbound climb out of the Coachella valley (Palm Springs).
With the vacuum hose disconected & plugged at the EGR the next pull was 8 inches of vacuum so I left it disconected from that time on.....
Better vacumm on the flat lands was also noted cruising down the super slab from (12-14 inches to 14 to 17 inches) which of course means mo'power along with better fuel mileage.
Of course your mechanical distributor settings (375 & 41 weights) were in play prior which are perfect....
When I sold the 87 RV I think the EGR vacuum was never reinstalled

Jim
kitabel
Contributor
Posts 291
04-07-10 07:53 PM - Post#1894730    

Missing: an engine with low vacuum, high overlap and high compression using full vacuum will have a tendency to hunt and stagger at certain combinations of throttle position and engine speed right above idle, making setting idle speed for auto trans very irritating.

Set idle speed to 700 with vacuum off.
Connect vacuum, extra advance raises speed to 1,000.
Set idle mix.
Scenario #1: if you touch the gas, the idle vacuum jumps, which spikes the vacuum canister and the RPM goes up way more than you intended.
You back off, but the vacuum goes higher momentarily, and the engine doesn't slow down. After 2-3 seconds, it does - and may stall.
Scenario #2: more throttle. Vacuum drops.
Can retards spark timing, which reduces vacuum, which retards spark timing, blah.
Result: soggy response in a narrow range of throttle motion above idle until RPM picks up.

Ported prevents the engine idle from being too "nervous" as to changes in idle vacuum. Yes, it generally requires more initial advance.

wayloud72
Forum Newbie
Posts 17
wayloud72
04-08-10 08:53 AM - Post#1894942    

Wow, some interesting stuff in here. Here's my thoughts... One comment was made about basically trying to get max advance at idle to try and fire the mix. How much advance do you want at idle? Also a comment was made on exhaust gas dilution. Now if that's an issue, you have so much overlap in the camshaft, that vacuum isn't really much of a worry for what you're doing. The whole idea of the vacuum advance was for mileage and will make the engine run cooler, am I not right? Anytime I set a motor up with whatever distributor I used (HEI, MSD, Stinger, etc.) I dropped it in, unplugged the vacuum and brought the motor up to around 3000 rpm. I use a dial-back timing light so I can set the timing at what I want. I want total mech. timing at 36 degrees to start, and tighten the distributor down (put in lighter springs if it's not in by then). Check the timing at idle and on HEI's it's usually around 18-20 degrees. If you're running a Holley carb, they are pretty much known to run really rich at idle unless you live below sea level! Unless you buy an aftermarket HP or someones other carb body with adjustable air bleeds (need to put smaller ones in, to to make it crisper at idle) Now maybe some people want full advance at idle, but with a small load it could cause detonation (looking at the plugs 'cuz you can't always hear it) but 18-20 initial is more than fine with me. I prefer ported vacuum because it's throttle controlled and I don't want the extra 12 or so degrees advance unless the motor is under NO load and cruising down the freeway. The next thing to do and really make it right is to phase in the distributor so it's not trying to fire the next cylinder. I'll explain how to if anybody wants to know.
"It's all about stance!"
http://www.chevytalk.org/fusionbb/showtopic.php?ti...

IgnitionMan
Valued Contributor
Posts 3197
04-08-10 07:52 PM - Post#1895281    

Ported vacuum sourcing does not work in early engines, only those with functional EGR systems, and that is that, period, proven time and time again, by not only me, but many others as well.

Dial back timing lights on any ignition system BUT digital distributor-less systems, do not accurately tell the timing.

LOTS of holes in the above post as far as correctly doing ignition curve setup. Sorry, that is just the FACTS of it.
C10 Sleeper
Valued Contributor
Posts 3426
C10 Sleeper
04-09-10 08:12 AM - Post#1895499    

I had a dial back timing light a few years ago I could never get it to work. I thought it would be a good short cut from using a timing tape. That thing is probably buried deep in the land fill where it belongs. I agree with ignitionman he knows his stuff and against my backwards way of thinking I tried setting up my ignition system his way and haven't had a problem more like big improvement. If I wouldn't have followed his way I would probably still be guessing at how to make my truck run better.
http://photobucket.com/C10Pictures

IgnitionMan
Valued Contributor
Posts 3197
04-09-10 05:50 PM - Post#1895832    

I keep everything above board, and public, and I don't really do much with stuff sent to me in private messages, like below.

"Wow! I got shot down! lol Hey, what I posted on there has always worked for me and my stuff has always run pretty good. I'm never closed off for great ideas or actually any ideas, I just never understood why you'd want full vacuum advance at idle. Maybe I'm missing something. Would be nice to sit down with coffee or a beer and toss some stuff around, 'cuz I do listen! What don't you like about those timing lights? If you have your front tab and damper set up at exact TDC, then where would it not work? If I'm missing something and can eek an extra 5hp out of my stuff, tell me! You ever do much with distributor phasing? The old fashioned way of drilling a hole in the cap and watching the rotor swing and making it even from side to side by adding or removing from the vacuum rod? Hope you have a great weekend and hope to talk to you soon. Brad p.s. You don't live in So Cal do you?"

No, I no longer live in So. Cal., I live in No. Nevada. I don't drink beer or coffee. And, YES, I do, do quite a lot of "phasing", as I am a person that does small body HEI conversions to points distributors (I perfected them), for a living. I also worked for Duntov at GM (engine development, includes ignition systems and curves), and, at Holley, and have been a professional mechanic for just at 38 years now, and inventor, etc.

Being a person that does things the right way, I don't have much patience for "runs pretty good". I do more fix it work on "runs pretty good" stuff, and it is getting very, very old.


steeler_fan
Contributor
Posts 142
steeler_fan
04-13-10 03:37 PM - Post#1897970    

All
I don't pretend to be an expert on this at all. but here are a few thoughts

1. you want vacuum advance at idle to keep the engine temps low. Pulling in advance does this unless you want to set you static advance high and ignore Vacuum advance.

2. i have found manifold vacuum works best, even on my smog engines. after switching to manifold i have been able to set my static timeing a little higher.
The end result was my car idled better ran cooler and also got a little better gas mileage. If i were do due things 100% right I would also reset the distributor total advance lower by the amount I set the static higher. But i haven't pushed the static too high, on my 72 buick i went from 4 to 8 TDC

3. to figure out what can you would want to use the first thing you should do is figure out what amount of vacuum you pull at idle when motor is hot. on my buddies 396 we found we needed a can that pulled the vacumm in a about 8 Hg. additionally since we set intial Static at 10 and measure 35 full in, we picked a can that only added 8 more degrees which based on notes above would give and end result of 16 for a total of 51.
Once we did this his car was much more streetable.

4. you need to figure out what the total advance your distributor has set and determine if you need to change this based in the can selciton. For example if have intial Static timing at 10 with the distributor total advance at 38, you would not want a can with a rating of 12 degress of advance. Remember the can rating will all 2x the vacuum. this would give you about 38+24 for total of 62 degrees when both Vacuum and Mechanical advance are present. either buy a can that only pulls in about 10 degrees or limit your total static from distrbutor to about 33.

5. one other decision you need to consider is how fast the centrifugal advance is pulled in. Example if static is 10,final is 35. do u want the 35 pulled in at 3000 RPM or 4000 RPM. On a car used for peformance runs you may want the advance to pull in early, in this case since you will on the throttle the hole time. the vaccum advance at the top end will not really kick in since you won't have vacuum from the manifold.

so many options.

I would love some day to take my distributor to a and old guy with a curve machine and dial in both my impala and Buick. but for now neither car has a ping a high load, and both run ok. But i know i still don't the optimum setups.

I hope this makes sense. again i don't pretend to be an expert, but i have tried to spend a lot of time reading this material to understand it in a simple way that my brain could digest

Steeler_fan

prgm_mgr
Member
Posts 532
05-04-10 10:10 AM - Post#1909773    

Hi all


I have a 58 Impala with a 348 stock motor and stock distributor. When setting up the initial location of the vacuum advance, does it matter which position it is in?

The book I am using says to start with the can at approximately 45 degrees to the engine, go back about 1/2 inch and move the can forward until the contact is broken (?) (I'm using a light bulb connected to the coil etc.When the light goes out, I'm in the right spot)

Anyhow, if I follow their advice, the can winds up directly over the distributor hold down bolt, making it difficult to tighten down without moving the distributor out of alignment.

Can I move the can closer to the fire wall such that the it is approximately 90 degrees to the engine, again adjusting it so the contact is broken? This leaves room to tighten the bolt.

What I think this also does is move the #1 spark plug wire spot on the distributor from the first spot left of the little door on the cap to the second. The rotor remains roughly at 6:30 on the cap.

Does this make sense?

Thanks for your advise
Mark


markamatic
Forum Newbie
Posts 24
01-11-15 06:28 PM - Post#2513947    

I want to tank you for your response to the Vacuum advance . I made a post here about my 427 heating at idle and it never ran like I felt a 427 should . Even though its in a full sized 69 CST long bed at 4500 lbs it should get out of its own way . I was a GM mechanic for many years and I knew the vacuum advance was critical to gas mileage and idle quality . I made a mistake by hooking it up to ported vacuum ! I hooked it up to manifold vacuum and my idle quality returned even with a mild cam . My heating problem vanished and my horsepower on take off went through the roof . That old truck will lay down 300 feet of posi marks if you can hold it straight !! Im a very happy camper now :0) thank you so much !
octanejunkie
Contributor
Posts 595
octanejunkie
01-11-15 07:05 PM - Post#2513963    

There's a tremendous wealth of knowledge here, especially in regards to timing and ignition. I learned everything I know about it on this here forum from guys like IgnitionMan; almost exclusively from him actually.

Now that I have a computer controlled distributor, and EFI, I can better appreciate seeing results instantly with the tap of a key rather than messing with weights and plates and springs and needles and such. Anyone wanna buy a well-tuned HEI distributor? He he he.

FWIW, I run 25° timing at idle and I've never seen more vacuum in park with as steady a needle, plus my truck launches and runs like a scalded mule. I still drive with a vacuum gauge and find it the most honest and reliable, realtime feedback I can get from my engine. Gotta love technology, old and new 😊
'59 Chevy 3100 Stepside
0.030-over 350, mild (214/224 @ .050) 112 LC cam,
vortec heads, air-gap, 600cfm carter, Holley Avenger EFI, 2-1/2" rams horns,
Bowtie Overdrives 700R4 w 2200rpm stall, 3.42 posi rear on top of 31.5" BFGs

65_Impala
Very Senior Member
Posts 3856
01-11-15 07:42 PM - Post#2513974    

  • octanejunkie Said:
FWIW, I run 25° timing at idle



I've got 28* at idle programmed into my LT1. That timing gives about the lowest injector pulse width. It could idle forever on the hottest day without overheating only using a 16" electric fan strapped to the radiator. And that fan doesn't even have to cycle on that much.

octanejunkie
Contributor
Posts 595
octanejunkie
01-11-15 08:20 PM - Post#2513985    

  • 65_Impala Said:
  • octanejunkie Said:
FWIW, I run 25° timing at idle



I've got 28* at idle programmed into my LT1. That timing gives about the lowest injector pulse width. It could idle forever on the hottest day without overheating only using a 16" electric fan strapped to the radiator. And that fan doesn't even have to cycle on that much.




Nice. I know I will have to re-tune it when the warmer weather comes to So Cal. 100°+ ambient temps make hot rods so much fun to manage.
'59 Chevy 3100 Stepside
0.030-over 350, mild (214/224 @ .050) 112 LC cam,
vortec heads, air-gap, 600cfm carter, Holley Avenger EFI, 2-1/2" rams horns,
Bowtie Overdrives 700R4 w 2200rpm stall, 3.42 posi rear on top of 31.5" BFGs

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